CDC's new estimation method raises H1N1 numbers

Nov 12, 2009 (CIDRAP News) – The US Centers for Disease Control and Prevention (CDC) today unveiled a new counting method that significantly increases the estimated numbers of pandemic HIN1 cases, hospitalizations, and deaths. At the same time, the agency said it will receive only about half the vaccine it expected this week.

At a media briefing today, Anne Schuchat, MD, director of the CDC's National Center for Immunization and Respiratory Diseases, said the CDC's new method of calculating pandemic cases and deaths is designed to provide a better big-picture view. Though the new numbers are significantly larger than the CDC's previous counts, they don't suggest that the disease situation has changed, she said.

Earlier this week a handful of influenza blogs and message boards, as well as media outlets such as the New York Times, previewed the new CDC estimates.

A broader way to view flu burdenThe new estimates combine information from the CDC's Emerging Infection Program Network, which tracks flu cases in 10 states and 62 counties, with aggregate state reports of lab-confirmed hospitalizations and deaths. Previous hospitalization and death counts were based on individual lab-confirmed cases. "We've tried this a few different ways, and really the estimates converge," Schuchat said. "We're feeling comfortable we'll be giving you appropriate estimates today."

The CDC numbers for April through Oct 17 give a single number for each category, plus lower and upper estimates around each number. She said the CDC estimates that 22 million people in the United States have become ill with the pandemic flu virus. The number of hospitalizations is estimated to be 98,000, with range between 63,000 and 153,000. For comparison, the CDC's most recent hospitalization count using the previous tracking method is 17,838.

Deaths through Oct 17 likely totaled 3,900, with a range of 2,500 to 6,100. For comparison, the CDC's most recent fatality count using its previous tracking method is 672. Pediatric deaths calculated with the new system total 540, with a range of 300 to 800. For comparison, the CDC's most recent pediatric death tally using its previous method was 129 lab-confirmed pandemic H1N1 fatalities.

Age-based breakdowns using the new method are available on the CDC's Web site and all the numbers will be updated every 3 to 4 weeks. Schuchat said the new estimation method confirms that younger people are bearing the brunt of pandemic illnesses and supports the prioritization recommendations set by the CDC's vaccine advisory committee.

Special concerns for diabetic patientsAt today's briefing, Schuchat singled out the impact that the virus is having on people with diabetes. So far, 12% of all hospitalizations for pandemic flu infections have involved people with the disease.

"We know that people hospitalized with H1N1 influenza who have diabetes have a good chance of ending up in the intensive care unit," she said. "One in four hospitalized patients with diabetes did require intensive care unit management."

The three most important measures people with diabetes can take to protect themselves against the virus are to receive the injectable version of the pandemic vaccine, check with a healthcare provider at the first sign of a flu-like illness for prompt treatment with oseltamivir or zanamivir, and ensure that they have received the pneumonia vaccine.

Vaccine production shortfallIn her update on vaccine developments, Schuchat said the number of doses available to states for ordering has now reached 41.6 million, which she said is lower than what federal officials expected. On Nov 6 when the vaccine supply stood at 38 million the CDC said if all production steps went smoothly for the manufacturers it expected the vaccine supply to grow by 8 million doses over the ensuing week, but today's figure marks an increase of only 3.6 million.

Schuchat said it's difficult to make accurate vaccine production projections from week to week, because some steps happen at the last minute, such as lot release testing before the vaccine leaves the plant. "If the lot releases come out a certain way, everything goes forward. If they come out other ways, you have to look into things in more detail," Schuchat said.

Sometimes problems crop up with shipping as vaccine leaves the factory, she said, adding that CDC officials have been told that hurricane-related disruptions might have contributed to some shipping problems this week.

A spokeswoman for MedImmune, the company making the intranasal, live attenuated H1N1 vaccine (LAIV), told CIDRAP News in an e-mail today that the company's delivery of nasal spray to the US Department of Health and Human Services (HHS) is in line with expectations. A spokesman from Sanofi also told CIDRAP News that the company is on track with pandemic vaccine delivery and that it delivered what it promised this week.

A Novartis spokeswoman said today that the company is on track with its commitment to the government. She said Novartis has shipped over 7.5 million doses of H1N1 vaccine and expects 25 to 30 million doses to become available by the end of November.

Schuchat said the CDC won't know until tomorrow what the week's final vaccine tally will be. "It's an imperfect process both producing the vaccine and then projecting how many doses you'll have at any one point," she said. "It's important for us all to remember it's a marathon and not a sprint. But more vaccine is being ordered, delivered, and used every day."